Science: Under the Hudson

Through solid rock, shifting sand,
sliding mud, two great shields are boring toward each other under the
Hudson River. When they have come together there will be a new
vehicular tunnel from Manhattan to New Jersey. The moment of their
marriage is, for the engineers in charge, the zero hour. The latter
will not know till then whether they have calculated perfectly this
blind meeting underground or whether their plans have gone awry.

Last week the shields were less than 500 ft. apart. In spite of their
huge weight, the distance they have...